Lubricant composition containing polycarboxylic acid

ABSTRACT

This invention is directed towards lubricant compositions comprising a lubricating oil and a corrosion inhibiting amount of a polycarboxylic acid containing at least four non-carboxylic carbon atoms and more than two carboxyl groups. These compositions, when based on synthetic ester oils, exhibit reduced tendencies to corrode metals used in construction of gas turbine engines, particularly, lead.

United States Patent 91 Bosniack et a1.

11] 3,719,600 March 6,1973

LUBRICANT COMPOSITION CONTAINING POLYCARBOXYLIC ACID Inventors: David S. Bosniack, Baytown, Tex.; Harold Shaub, New Providence, NJ. v

Esso Research and Engineering Company, Linden, NJ.

Filed: Feb. 8, 1971 Appl. No; 113,741

Assignee:

US. Cl ..252/56 S, 252/56 R, 252/57 Int. Cl. ..C10m 1/26, ClOm 1/24 -Field of Search ..252/56 D, 56 R, 56 S, 57

References Cited UNITED STATES PATENTS 9/1954 Sirianni et al. ..252/57 8/1962 Tierney et a1 ..252/57 X 3,090,753 5/1963 Matuszak et al. ..252/56 S 3,180,832 4/1965 Furey '.....252/56 R 3,218,353 11/1965 Volkenburgh et a1. ...260/5 14 2,334,158 11/1943 Fuchs et a1 .L...252/56 D X OTHER PUBLICATIONS Chemical Abstracts, Vol. 53 1959) C01. 9232b Primary Examiner-Daniel E. Wyman Assistant Examinefl-W. Cannon Attorney-Pearlman & Schlager and Carl G. Seutter [57 ABSTRACT 12 Claims, No Drawings LUBRICANT COMPOSITION CONTAINING POLYCARBOXYLIC ACID BACKGROUND OF INVENTION engines.

2. Description of Prior Art The admixture of small amounts of certain materials to natural and synthetic lubricating oils to modify their properties in desirable ways is well known to those skilled in the art. Thus, for example, dispersants have been added to reduce the tendency of an oil to form engine' sludge, and antioxidants have been added to improve the resistance of an oil to oxidative deterioration.

Other additives have also been used to reduce the tendency of an oil, during and after prolonged storage,

to corrode metals with which it may come in contact, particularly, lead. Many gas turbine engines, such as those used to power modern aircraft, contain bearing cages having lead flashings. Lead corrosion, therefore, must be held to a minimum in such engines. Upon prolonged periods of storage, lubricants undergo deterioration and develop a tendency to corrode metals such as lead. Because of the need to stockpile synthetic lubricating oils around the world in a variety of climates for prolonged periods, the U.S. Air Force has included storage stability requirements in specifications for oils.

While prior art materials have proved useful in lubricating oils meeting these specifications, efforts have continued to find more effective additives which Viscosity at 210F. SUS 44 Viscosity at 100F. SUS I68 Viscosity Index 91 2 An SAE 3i) Pennsylvania type lubricating oil with the following flow properties:

Viscosity at 210?. sus

3. An SAE 30 Naphthenic solvent-refined lubricating oil with the following properties:

Viscosity at 2l0F. SUS 58 Viscosity at [00F. SUS 510 Viscosity Index 62 Other such oils useful in the practice of this invention are well-known to those skilled in the art.

The synthetic lubricating oils which may be improved by use of this invention may include liquid, high molecular weight esters, fluorocarbons, polyethers, and polysilicones, etc.

Typically, the synthetic oil may be an ester formed by the reaction of (a) a C -C aliphatic acid R (COOH), wherein R is an aliphatic hydrocarbon (including inertly-substituted hydrocarbon) residue and n is typically l3,,preferably l, with (b) a C -C aliphatic alcohol R"(0l-I)m wherein R" is an aliphatic hydrocarbon (including inertyl-sub'stituted hydrocarbon) residue and m is an integer, preferably 1-6, more preferably 14, most preferably 3-4.

impart improved properties to the oils they are used to treat. g

It is an object of this invention to provide a novel lubricant composition. Other objects will be apparent to those skilled in the art from the following description.

SUMMARY OF THE lNVENTlON In accordance with certain of its aspects, the lubricant composition of this invention may comprise:

a. a lubricating oil; and 7 b. a corrosion-inhibiting amount of a polycarboxylic acid of the formula R cooH' The mostpreferably, however, are enanthic and pelarwherein R is an acyclic hydrocarbyl nucleus having at least four carbon atoms and x is an integer greater than 2. i

Description of the Invention I In accordance with certain of its aspect, the lubricating oils which may be irn proved by this invention may include various lubricating oils such-as naturally- The base oil may, in one embodiment, bea liquid ester product of an aliphatic monocarboxylic acid and a polyol. The preferred of these acids may be C -C ll-, lustrative of such acids may be:

valeric C, pivalic C, dodecanoic C stearic C "eicosanoic C triacontanoic C hexatriacontanoic C Preferably C6-C acids may be used. Typically of such acid may be:

caproic acid C. caprylic acid C, capric acid C enanthic acid C, pelargonic acid C Z-ethylhexanoic acid C.

gonic acids.

The polyols which may be reacted with the noted aliphatic mono'carboxylic acids, to form esters, may include R"(OI I)m wherein R" is an aliphatic hydrocarbon moiety and m is an integer preferably 2-6, more preferably 2 4. The preferred polyols may be the C2 00, say C2-C4 polyols. Typical may be:

neopentyl glycol trimethylol ethane trimethylol propane trimethylol butane pentaerythritol dipentaerythritol Thepreferred glycol may be pentaerythritol.

of such polyols;

including the following illustrative examples:

pentaerythritol tetra-valerate pentaerythritol tetra-caproate pentaerythritol tetra-pelargonate pentaerythritol tetra-butyrate dipentaerythritol hexa-valerate dipentaerythritol hexa-pelargonate depentaerythritol hexa-caprate trimethylol propane tri-caproate trimethylol propane tri-butyrate trimethylol propane tri-valerate trimethylol propane tri-pelargona'te The preferred. esters may be pentaerythritol tetracaproate.

In another embodiment, the liquid synthetic ester may be the product of reaction of an aliphatic polycarboxylic acid and an aliphatic monohydroxy alcohol.

Preferably, the aliphatic polycarboxylic acid may have the formula R"(COOI-l)n wherein n is greater than 1 and preferably 2-3. Typical polycarboxylic acids may include:

adipic acid azelaic acid sebacic acid dodecanedioic acid succinic acid 1,2,4 butane tricarboxylic acid Preferred acids may be adipic and azelaic.

Preferably the alcohol may have the formula R"OI-I where R" may be a saturated aliphatic group which may be inertly substituted. Typical alcohols may include methanol, n-butanol, 2-ethyl-n-butanol, pentanol,l-hexanol, 2-ethyl-hexanol, l-decanol, 2-ethyloctanol, and 2-ethoxy ethanol.

Specific illustrations of this type of synthetic ester lubricating oils which may be used in this invention are:

TABLE I di-Z-ethylhexyl sebacate di-2-ethylhexyl azelate di-Z-ethylhexyl adipate di-n-amyl sebacate di-Z-ethyl octyl succinate di-2-ethoxyethyl sebacate di-2-ethyl octyl adipate di-2-ethyl octyl azelate tri-pentyl-l ,2,4 butane carboxylate Preferred esters may be di-Z-ethylhexyl azelate and di- Z-ethylhexyl adipate.

These oils may be blended with other synthetic-esters as noted supra or with other oils, such as caster oil; lard oil; polymerized olefins; copolymers of alkylene glycols or aliphatic alcohols with organic acids, etc.

The lubricant compositions of the present invention may preferably contain other additives, typically present in amount of 0.001 wt. %,including:

a. oxidation inhibitors such as aromatic amines e.g.

phenothiazine; Y b. metal corrosion inhibitors such as benzo-triazole; c. metal passivating and load-carrying agents, such as tricresyl phosphate; d. anti-foamants such as a silicone;

e. dispersants such as the polymethacrylates.

In the practice of this invention, according to certain of its aspects, there may be added to said lubricating oil a corrosion-inhibiting amount of a polycarboxylic acid 5 .of the formula:

R(CO OH), (I) wherein R is'an acyclic hydrocarbyl nucleus having at least four carbon atoms and x is an integer greater than 2.

The corrosion-inhibiting amount of polycarboxylic acid may be sufficient to decrease corrosion, and particularly corrosion of lead, by the lubricant composition to a satisfactory level. Commonly, this may mans a reduction-in lead corrosion to a point at which the lubricantc'omposition satisfies specifications such as those set by the U.S. Air Force as for example in MIL-L-7808G. There may be present 0.01 to 1.0 parts, preferably 0.0l5-to 0.5 parts, most preferably 0.02-0.05 parts of polycarboxylic acid per 100 parts of lubricating oil.

In the formula (I), R(COOI-I),, x may be an integer greater than 2, typically 3-7, preferably 3-4, say 3; R may be a hydrocarbyl moiety containing at least four carbon atomsQtypicaIly an alkyl group. R may be n-butyl, isobutyl, t-butyl, pentyl, neo-pentyl, hexyl, isodecyl, n-octadecyl, 3-ethyl-nonadecyl, etc. The R group may contain inert sub-stituents which are inert under the conditions of operation of the invention, such as aryl, alkaryl, aralkyl, alkoxy, etc. substituents.

In the preferred embodiment of this invention, R of Formula I may be:

5 5 wherein n is an integer at least four.

cally 3-6, say 3. If x be, e.g. 4, the acid may be, inter alia, n-octane-l ,2,4,6-tetracarboxylic acid n-decanel ,2,3 ,4-tetracarboxylic acid n-heptane-4-phenyl-l ,4,6,7-tetracarboxylic acid n-pentane-3-ethyl-l -,2,4,5-tetracarboxylic acid, etc. Ifx be, e.g. 5 the acid may be, inter alia,

n -pentane-3(n-pentyl)-l ,l ,3,5,5-pentacarboxylic acid I n-decane-2,4,6-methyll ,l 5,7,9-penta-carboxylic acid n-nonane-S-phenyll ,2,5 ,8,9-pentacarboxylic acid,

etc. In a typical preferred embodiment of this invention,

n-hexane-l,3,6-tricarboxylic acid. Most preferably,

however, the acid is n-pentane-l ,3,5-tricarboxylic acid, (i.e. octric acid).

In Formula 1: may be an integer greater than 2, typitricarboxylic acid, n-pentane-2,3,4-tricarboxylic acid,

This invention may be practiced using mixtures of the above described acids. For example a mixture of 1-10 parts of octric acid per 1 part of n-heptane-1,4,7--

tricarboxylic acid may be employed. Other such mix tures will be obvious to those skilled in the art.

The acids which may be used in the practice of this invention may be readily available from natural or commercial sources or they may be synthesized by well-known procedures such as hydrolysis of nitriles derived from appropriately substituted halogenated starting materials. For example, octric acid may be prepared from 4-bromo pimelic acid according to the following scheme:

Other such synthetic routes will be apparent to those 0F., preferably 200-220F. Mixing may be continued I over a period of 5 to 120 minutes, preferably 20 to 60 minutes, say 30 minutes.

it is a feature of this invention that the lubricant composition may be formulated from a concentrate of the polycarboxylic acid. Typically, such concentrates may contain 0.1 to 50 parts, preferably 0.1-10 parts, say 0.5 to 5 parts of acid in 100 parts of lubricant-composition soluble diluent solvent.

The diluent-solvent may be an inert liquid in which the acid may be soluble or dispersible. Commonly, the solvent may be an inert liquid having a boiling point of about 50--250C., say 75-l50C.

The diluent-solvent may be characterized by its solubility or dispersability in lubricants. Typically, the diluent-solvent may be a'low molecular weightmineral oil, polyether, a fluorocarbon, or preferably, a lubricating oil.

The diluent-solvent may include low molecular weight mineral oils such as solvent 150 neutral oil, solvent 325 neutral oil, and bright stock. Polyethers which may be employed as diluent-solvent include 1,2- dimethoxy ethane; 1,5-diethoxy-3-oxa-pentane; and l,8-diethoxy-3,S-dioxa-octane. Fluorocarbon liquids which may be used as diluent solvents include perfluorooctane, perfluorotetradecane, perfluoro-octadecane and perfluorobenzene.

In a preferred embodiment, the diluent solvent may be a lubricating oil and most preferably it may be the oil forming the base of the lubricant composition.

Thus, the concentrates prepared in accordance with this invention may typically contain the following:

TABLE ll Broad Range Preferred Range Typical Acid 0.1--50- 0.1-l0 0.5-5 Diluent-solvent l-l00 l-50 10-50 A preferred concentrate may contain 4 parts acid in 100 parts diluent-solvent. Typically such concentrates may include:

1. 1.0 part octric acid, 100 parts pentaerythritol tetracaproate 2. 1.0 part octric acid, 100 parts di-(Z-ethylhexyl) adipate 3. 1.0 part octric acid, 100 parts di-(2ethylhexyl) sebacate 4. 1.2 parts octric acid, 100 parts di-(Z-ethyloctyl)adipate.' 1 The novel process of this invention permits attainment of outstanding results in lubricant compositions such as the following illustrative formulations FORMULATION A Component Parts Di(2-ethylhexyl) azelate 100 Di-(octylphenyl) amine L0 Phenyl alpha naphthyl amine 0.8 Tricresyl phosphate 0.6 Hydroxy terminated ester of linoleic 7 acid dimer 0.5 Alkyl methacrylate-n-vinyl pyrrolidone 0.5 copolymer (M01. Wt. 850,000)

FORMULATION B Component Parts di-2-ethylhexyl adipate di-isodecyl adipate 30 di(octylphenyl )arnine 1.0 phenyl nlphu naphthyl amine 0.8 tricrenyl phottphute 0.6 hydroxy terminated ester of linolcit: acid dimer 0.5 alkyl methacrylate n-vinyl pyrrolidone copolymer (MoLwt. 500,000) 1.0

To such formulations as A and may also be added various additives such as a primary amine of a C tertiary alkyl group, e.g.

CaHm- NH2 hereafter referred to as Additive B or a mixed methyl, butyl phosphate ester salt of an alkylated aryl, amine,

C(HDO ly, and a lead corrosion test is carried out on each sample. In the lead corrosion test a sample of oil is agitated while in contact with copper and lead plates for 60 minutes at 325F. while air is bubbled through the oil. At the end of the test, the loss in weight of the lead plate is determined.

Results are reported as milligrams lost (or gained) per square inch of exposed plate. The specification requires that an acceptable formulation exhibit a maximum of 25 mg/in LOSS (or gain) after 48 hrs. Storage. The novel compositions of this invention permit attainment'of outstanding results when subjected to this test.

It is a feature of this invention according to one of its aspects, that the lubricant composition permits lubrication or rubbing parts by contacting a first part to be lubricated with said lubricant composition, and rubbing said part against a second part.

Description of Preferred Embodiment Practice of this invention will be apparent to those skilled in the art from the following examples, wherein, as elsewhere in this specification and claims, all parts are parts by weight unless otherwise specified;

In a first series of examples, a standard formulation of lubricating oil (Formulation C) was prepared:

FORMULATION C Component 7 'Parts Adipic Acid coester of C oxo, C oxo alcohols 100.0 di(octylphenyl) amine l.0 phenyl alpha naphthyl amine 0.8 tricresyl phosphate 0.6 hydroxy terminated ester of linoleic acid dimer 0.5 oct'yl methacrylate-n-vinyl pyrrolidone copolymer (Mol. Wt. 850,000) 0.5 benzotriazole 0.02 Additive A 0.05

In each of the Examples 1 through 8, there was added to Formulation C, a corrosion inhibiting amount of a polycarboxylic acid (according to this invention) or as a control, a comparable amount of an acid used in the prior at for lead corrosion inhibition but falling outside the scope of this invention. These lubricant compositions were then evaluated in a standard test, MIL-L-7808, as described above. v

The following Table summarizes the acids used and their amount and the change in weight of the lead recorded during the test:

6 example octric 0.025 0.89 7 example octric 0.02 0.04 3.05 8 example octric 0.02 0.02 9 example octric 0.05 0.05

In mg.'per square inch of coupon exposed.

From the results summarized in this Table, it can be seen that when the oil is treated in accordance with this invention as in Examples 6-9, corrosion of lead falls within the range of 0.89 mg/in (Example 6) to 0.02 mg/in (Example 8), a decrease of 40-200 fold. In base Example I, the corrosion was 39.5 mg/in.". Furthermore, storage of the oil for a longer time before test, i.e. 168 hours, produces even more dramatic evidence of the utility of this invention. Under these conditions, the corrosivity of the oil is reduced by a factor of 300 when treated in accordance with this invention (Example 2 versus Example 7).

In second series of examples the effect of the 0.02 part of preferred octric acid on Formulation A so described above, was determined. The results are summarized in the following Table:

TABLE IV Purpose Octric Acid Example Lead Wt. Loss,

mg/in I68 I-Irs. Storage 10 base none 6.56

l 1 example 0.02 0.036

As can be seen the addition of 0.02part of octric acid to Formulation A desirably reduces its lead corrosivity by a factor of about 200-fold.

In a third series of examples, Formulation A as that described above as Additive A and present in a concentration 0.05 part per parts of base azelate ester. The results of these tests are summarized in the following table.

TABLE v Addi- Lead Wt. Loss, mg/in. Purpose Acid tive A 48 Hrs.Stg. I68 I-Irs. Stg. 12 base yes 33.79 69.40 '3 example octric yes 0.042 29.1 14 control citric yes I62 17 l .8 15 control NTA yes 54.3 89.2 ,6 control TCA yes 8.77

l08.6 (a) NTA nitrilotriacetic acid; (b) tricarballylic acid From comparison of Examples 12 and 13, it canbe pared with base Example 12 demonstrate that tricarboxylic acids not within the scope of this invention fail to reduce the corrosivity of an oil towards lead after 168 hours storage.

In a fourth series of examples (Examples 17-24), Formulation A as described above was blended with varying amounts of the two additive, Additive B, as described above, and Additive A, as described above. Then 0.02 part of eitheroctric acid (Examples 18, 19, 22, and 24) or sebacic acid (Example 20) was added to certain formulations. As can be seen from inspection of the following Table in every instance where the preferred octric acid was used, corrosivity of the oil toward lead was markedly reduced while when sebacic acid was used (Example 20) no such effect was observed.

TABLE VI Amount Amount Lead WLLoss, mg. ex.

Purpose Addi- Addi- Acid After After tiveB tiveA 48 Hrs. l68l-lrs. Storage Storage 17 Base 0.0175 0.05 41.1 105.1 18

Example 0.0175 0.05 Octric 0.00 16.2 19

Example 0.012 0.034 Octric 4.23 49.47 20 Control 0.012 0.034 Sebacic 6.04 88.4 21

Base 0.014 0.04 24.6 22

Example 0.014 0.04 Octric 0.012 23 Base 0.01 0.028 29.2 24

Example 0.01 0.028 Octric 0.042

As can be seen from comparison of Example 17 with Example 18, Example 21 with Example 22 and Example 23 with Example 24, the addition of octric acid to an oil desirably reduces its corrosivity towards lead by as much as a factor of 2000-fold. Use of sebacic acid on the other hand (Example 20) was found to be less than half as effective as octric acid (Example 19).

In a further series of experiments (Examples 25-28) the relative effectiveness of octric acid and sebacic acid were evaluated in oils based on Formulation B, as described above, having varying amounts of the above described Additive B and Additive A. The results of these tests are summarized in the following Table.

TABLE VII Amount Amount Lead Wt.Loss, mg.

Purpose Addi- Addi- Acid After After tive B tive A 48 Hrs. 168 Hrs. Storage Storage 25 Base 0.0175 0.05 30.8 26

Example 0.0175 0.05 Octric 0.021 0.104 27 Example 0.012 0.034 Octric 4.77 2.50 28 Control 0.012 0.034 Sebacic 19.8 58.2

' Concentration 0.02 part.

Comparison of Examples 25 and 26 again shows that addition of octric acid to an oil desirably reduces its ability to corrode lead by a factor of l000-fold. In contrast, addition of sebacic acid is found to be undesirably less effective by a factor of as much as 20-fold (Examples 27 and 28).

Similar improved results may be obtained by practice of this invention by use of the following specific acids:

Example Acid 29 n-butane-l ,2,3-tricarboxylic acid 30 3-methy1-pentane 1,3,5-tricarboxylic acid 31 n-heptane-l ,4,7-tricarboxylic acid 32 S-phenyl-n-nonane 1,5,9-tricarboxylic acid Example 33 A concentrate prepared in accordance with this invention may be prepared by adding 0.1 2.0 parts of octric acid to parts of di-(2-ethyl hexyl) azelate and adding 0.0] to 0.2 part of this concentrate to the Formulation A described above.

Although this invention has been illustrated by description of specific embodiments, it will be apparent to those skilled in the art that many changes and variations can be made which clearly fall within the scope of this invention.

What is claimed is:

1. A lubricant composition comprising:

a. a major amount of a lubricating oil; and

b. a minor but corrosion inhibiting amount of a polycarboxylic acid of the formula R(COOH wherein R is an acyclic hydrocarbyl nucleus having four to 21 carbon atoms, and x is an integer between 3 and 7.

2. A lubricant composition as claimed in claim 1 wherein said acid is of the formula wherein n is an integer between 4 and 21.

3. A lubricant composition as claimed in claim 1 wherein said oil is a synthetic ester lubricating oil.

4. A lubricant composition as claimed in claim 1 wherein said acid is pentanel ,3,5 tricarboxylic acid.

5. A lubricant composition as claimed in claim 1 wherein said'acid is present in the amount of about 0.01-1.0 part per 100 parts of said oil.

6. A lubricant composition comprising:

a. about 99.9 99.98 parts of a synthetic ester lubricating oil, and

b. about 0.1 0.02 parts of pentane l,3,5-tricarboxylic acid.

7. A concentrate for treating lubricant compositions which comprises a. l to 100 parts of a lubricating oil, and

b. 0.1 to 50 parts of a polycarboxylic acid of the for mula R(COOl-l wherein R is an acyclic hydrocarbyl nucleus having four to 21 carbon atoms .1: is an integer between 3 and 7, and the lubricating oil is present in lubricating amounts.

8. A concentrate as claimed in claim 7 wherein the lubricating oil is synthetic ester lubricating oil.

9. A concentrate as claimed in claim 8 wherein the lubricating oil is present in 99.8 parts.

10. A concentrate as claimed in claim 7 wherein the acid is pentane 1,3,5-carboxylic acid.

11. A concentrate for treating lubricant compositions comprising a. about 95.0 99.9 parts of a synthetic ester lubricating oil, and b. about 0.1 5.0 parts of a polycarboxylic acid of the formula R(COOH) 

1. A lubricant composition comprising: a. a major amount of a lubricating oil; and b. a minor but corrosion inhibiting amount of a polycarboxylic acid of the formula R(COOH)x wherein R is an acyclic hydrocarbyl nucleus having four to 21 carbon atoms, and x is an integer between 3 and
 7. 2. A lubricant composition as claimed in claim 1 wherein said acid is of the formula CnH(2n 2 x)(COOH)x wherein n is an integer between 4 and
 21. 3. A lubricant composition as claimed in claim 1 wherein said oil is a synthetic ester lubricating oil.
 4. A lubricant composition as claimed in claim 1 wherein said acid is pentane-1,3,5 tricarboxylic acid.
 5. A lubricant composition as claimed in claim 1 wherein said acid is present in the amount of about 0.01-1.0 part per 100 parts of said oil.
 6. A lubricant composition comprising: a. about 99.9 - 99.98 parts of a synthetic ester lubricating oil, and b. about 0.1 - 0.02 parts of pentane 1,3,5-tricarboxylic acid.
 7. A concentrate for treating lubricant compositions which comprises a. 1 to 100 parts of a lubricating oil, and b. 0.1 to 50 parts of a polycarboxylic acid of the formula R(COOH)x wherein R is an acyclic hydrocarbyl nucleus having four to 21 carbon atoms x is an integer between 3 and 7, and the lubricating oil is present in lubricating amounts.
 8. A concentrate as claimed in claim 7 wherein the lubricating oil is synthetic ester lubricating oil.
 9. A concentrate as claimed in claim 8 wherein the lubricating oil is present in 99.8 parts.
 10. A concentrate as claimed in claim 7 wherein the acid is pentane 1,3,5-carboxylic acid.
 11. A concentrate for treating lubricant compositions comprising a. about 95.0 - 99.9 parts of a synthetic ester lubricating oil, and b. about 0.1 - 5.0 parts of a polycarboxylic acid of the formula R(COOH)x wherein R is an acyclic hydrocarbyl nucleus having between four and ten carbon atoms and x is an integer between three and six. 